The present invention relates to a method for repairing components of a gas turbine made of a super alloy as well as a corresponding solder alloy therefor.
A wide variety of methods for repairing components of a gas turbine and in particular components of gas turbines for use in aircraft (aircraft turbines) is known from the prior art. Example of these are described in U.S. Pat. No. 5,705,281, U.S. Pat. No. 5,561,827, U.S. Pat. No. 5,628,814, U.S. Pat. No. 6,503,349, EP 1 258 312 A2, WO 2007/031400 A1, EP 1 790 745 A1, U.S. Pat. No. 5,066,459, U.S. Pat. No. 5,182,080, U.S. Pat. No. 5,666,643, US 2005/0274009 A1, KR 1020010104662 A, EP 0 800 889 B1, US 2006/0134454 A1, GB 2 409 210 A, EE DE 699 20 257 T2, EP 1 197 290 A2, EP 1 818 132 A2, DE 32 37 776 C2, CA 2 496 189, CA 2 520 681, CA 2 581 908, US 2006/0174482 A1 and US 2006/013717 A1.
However, the disadvantage of the methods and repair materials described there is that for the most part, the repair materials are suitable only for specific substrate materials and have been coordinated for the materials, and involved individual processes must be carried out during the repair method to repair individual types of damage, making repair as a whole very expensive.
Therefore, the object of the present invention is providing a method for repairing components of a gas turbine, in particular an aircraft turbine, on the basis of super alloys, which can be carried out effectively and be used variably. Overall, the expense for executing repair work is supposed to be thereby reduced, wherein the quality of the repaired components is supposed to be maintained at a high level in accordance with requirements.
The invention proceeds from the knowledge that a simplified repair method may be provided for the different kinds of damage which may occur in the case of components of gas turbines, especially aircraft turbines, such as, for example, punctiform damage in the form of holes or the like, linear imperfections, such as cracks and the like, or planar defects, such as material removals, etc., in that the different kinds of damage are not repaired separately using individual methods, but together by using a common solder and/or a solder alloy for the repair. In doing so, the planar material removals are corrected by soldering on a molded repair part, while the punctiform or linear defects, such as holes, stripped cooling air holes, cracks and the like, are repaired by filling with the corresponding solder and/or the corresponding solder alloy. The solder and/or the solder alloy may therefore be used in a single work step for soldering on a molded repair part as well as for mending hole sites, stripped cooling air holes and cracks.
In the case of the present invention, solder alloy is understood to be an alloy, which has a NiCoCrAlY alloy and a Ni-based solder, while solder is understood merely as the Ni-based solder as a component having a low melting point. The NiCoCrAlY alloy supplies the required oxidation resistance and mechanical strength, while the Ni-based solder supplies the adhesive bond of solder alloy in the form of a matrix for the embedded NiCoCrAlY particles and for the component to be repaired.
The invention provides for making a molded repair part made of the solder alloy available for the repair of planar defects, such as, for example, in the case of a planar material removal, and for sealing additional punctiform or linear defects, such as cracks, holes and the like, by applying the solder and/or the solder alloy. The molded repair part in this case is also soldered on by the solder and/or the solder alloy, wherein, because the molded repair part is formed of the solder alloy, it is able to adhere directly to the substrate without additional application of the solder and/or the solder alloy. While the use of the Ni-based solder to connect the molded repair part to the component to be repaired or to fill in imperfections in the component to be repaired is conceivable, the use of the solder alloy is preferred, wherein the solder alloy in particular may be used both for sealing holes, cracks or small planar material removal and as the molded repair part, and wherein the molded repair part may in turn be soldered directly on a damaged planar spot without an additional binding agent, i.e., without additional solder or solder alloy. The solder alloys for the direct soldering of punctiform or linear imperfections and for the molded repair part may vary slightly with a basically similar composition with respect to the composition of elements and/or proportions. In particular, solder alloys may be used in which the same components or elements are included in slightly different proportions.
The component to be repaired that is correspondingly provided with solder and/or solder alloy or the molded repair part component is then subjected to a single heat treatment to form the solder connection, wherein both the molded repair part is soldered onto the component and the imperfections, which are filled with solder and/or solder alloy, are correspondingly tightly and securely sealed.
The solder alloy is aligned in such a way that both the Ni-based super alloys as well as the Co-based super alloys may be treated accordingly. As a result, universal use is possible in the case of gas turbines and in particular in the case of aircraft turbines.
The solder and/or the solder alloy may be applied to the component as a powder or powder mixture with or without a binding agent. Organic binding agents or other binding agents that evaporate or are removed by burning during the subsequent heat treatment for soldering may be considered as binding agents.
Accordingly, the molded repair part may be formed by a powder mixture of the solder alloy with or without binder, wherein corresponding techniques may be used for formation, such as, for example, pressing and the like.
The molded repair part may be applied as a corresponding green compact directly to the component to be repaired, or be sintered prior to application. In particular, a multi-stage temperature treatment process with different hold temperatures and hold periods may be provided as a sintering process.
In the same way, the heat treatment for forming the solder connection is a multi-stage heat-treatment process having different hold temperatures and hold periods.
The NiCoCrAlY alloy, which is used as a constituent of the solder alloy, may have a composition of 9 to 16% by weight, in particular 11 to 14% by weight and preferably 12.5 to 13% by weight aluminum, 18 to 25% by weight, in particular 20 to 24% by weight and preferably 22.5 to 23% by weight cobalt, 15 to 20% by weight, in particular 17 to 19% by weight and preferably 17.5 to 18% by weight chromium as well as 0.1 to 1% by weight, preferably 0.3 to 0.7% by weight and in particular 0.55 to 0.6% by weight yttrium. The remainder is formed by nickel and unavoidable impurities.
According to the invention, the Ni-based solder has at least a chromium content of 15% by weight and at least an iron and/or tungsten content of 15% by weight. The cobalt content may be limited to a maximum of 25% by weight. Due to the correspondingly high chromium content, there is good resistance to oxidation and corrosion.
The Ni-based solder, which is likewise a constituent of the solder alloy, may have a composition of 15 to 25% by weight, in particular 19 to 23% by weight and preferably 21.5 to 22% by weight iron and/or tungsten, a maximum of 10% by weight, preferably a maximum of 5% by weight, in particular a maximum of 2.5% by weight cobalt, 15 to 25% by weight, in particular 20 to 23% by weight and preferably 20.5 to 21% by weight chromium, 7 to 11% by weight, preferably 8 to 10% by weight and in particular 9 to 9.5% by weight molybdenum, 4 to 8% by weight, in particular 5 to 7% by weight and in particular 6 to 6.5% by weight silicon. The remainder is again formed by nickel and unavoidable impurities.
The NiCoCrAlY alloy and the Ni-based solder may be provided with proportions of 30 to 70% by weight of the NiCoCrAlY alloy, in particular with a proportion of 40 to 60% by weight in the solder alloy, while the Ni-based solder may have a weight proportion of 30 to 70% by weight and in particular 40 to 60% by weight. The solder alloy may preferably have a higher solder proportion for mending punctiform and/or linear imperfections, while the molded repair part may have a higher proportion of the NiCoCrAlY alloy.
Additional advantages, characteristics and features of the present invention will become clear from the following detailed description of exemplary embodiments on the basis of the enclosed drawings. In this case, the drawings show the following in a purely schematic manner: